Most airplane designers put the spar at or close to the recommended CG. This helps to ensure the lifting forces are acting at the strongest part of the wing. The center of lift is also typically at the thickest part of the airfoil, which again, is normallywhere the spar is located, as it allows them to build a stronger wing with fewer parts.

Yes you can use the measurements and the website, and it works very well. But as a spot check at the field before I fly any plane, I've found using the spar as the check point has been 100% effective.

Brad